Directional boring machines are used to drill holes underneath roads and other obstructions for the installation of gas lines, telephone and electrical cable and other utilities. In the past, installing a gas line or electrical cable across, for example a roadway, required excavation of a trench through the which the utility line was installed. After installation, the trench was backfilled with appropriate material, such as sand, in a series of stages. A layer of fill material was placed in the trench and tamped down, either manually or with a mechanical tamping device. This process was repeated until the trench was filled to a level close to the surface. At this point, the surface of the roadway would be resurfaced with gravel, asphalt, or concrete, depending upon the particular circumstances.
There has been a need for a means of boring under or through obstructions such as roadways, concrete lined waterways and large underground utilities to provide a passageway for utility lines without the need for trenching through or excavating around the particular obstruction. This need has been partially met by the development of a variety of directional boring systems for the installation of underground lines and conduits.
The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful hydraulic device such as a hydraulic cylinder. See Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated and the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water or mud to assist in boring. More recently, directional boring systems have been devised that can drill through rock. See Runquist et al., U.S. Pat. No. 5,778,991, issued Jul. 14, 1998, and Cox European Patent Publications EP 857,852 and EP 857,853.
Since accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool, a sensor and transmitting device (a sonde attached to the cutting tool is almost inevitably required to prevent mis-boring and re-boring.) One such device is described in U.S. Pat. No. 5,633,589, the disclosure of which is incorporated herein for all purposes.
Back reamers are commonly used in directional boring to widen the initial bore. According to one known method, a boring head and sonde housing are attached to the front end of a drill string by means of an adapter known as a starter rod, and the machine is then operated to bore through the earth. Additional drill string sections are added as the boring head moves further away from the hydraulic machine that drives it. The head, sonde housing and starter rod eventually emerge at the end of the run at an exit pit or site. The sonde housing is then decoupled from the starter rod, and the sonde housing and boring head are replaced by a back reamer, which is then drawn backwards through the initial bore in order to widen it.
This method has proven effective, but difficulties have arisen when it comes time to decouple the sonde housing from the starter rod. There are two known systems for connecting the front end of starter rod to the rear end of the sonde housing. One is a hex collar connection that is safe but does not provide a reliable connection. According to this approach, a front end of the starter rod is coupled directly to a conical threaded male member at the end of the leading drill rod. The other end has a cylindrical threaded recess that engages a threaded projection at the rear end of the sonde housing. The outer surface of the rear end of the starter rod is hex shaped, as is a shoulder portion of the sonde housing. The starter rod is threaded onto the sonde housing and tightened to the point where the hex surfaces line up, which is just short of full tightness. Then a sleeve for passing torque having a hex shaped opening is slid over both hex surfaces and secured in place using a set screw which is inserted through a hole in the sleeve and engages a threaded hole in the outside of the starter rod.
This coupling suffers from the increased diameter of the sleeve, which becomes the largest diameter part of the head and thus reduces boring effectiveness. It also has poor resistance to side loading, resulting in breakage of the joint during the run, often causing the boring head and sonde to be lost and abandoned in the ground at great cost. The other is a direct threaded connection between the starter rod and sonde housing which is secure but extremely difficult to uncouple after use due to the extremely high torque generated by the directional boring machine. Conventional practice, although contrary to manufacturer recommendations, is to have a workman working on the connection with a pipe wrench at one end of the bore while the machine operator back at the other end of the bore (often 1000 feet away) tries to unscrew the connection by reversing the rotation of the drill string. When the connection gives way, it doe so violently under a huge torque, often causing the wrench to break or fly off at high speed, with the possibility of serious injury to workmen nearby.
A strong, reliable joint that can nonetheless be easily uncoupled without having to use the directional boring machine is sorely needed. The present invention provides a joint which has great strength, yet can be uncoupled with simple hand tools when a bore is completed.